1. Field of Invention
The present invention relates to the field of safety inspection technology, in particular to an ion storage system and method for inspection equipment for inspecting drugs and explosives by means of ion mobility technique.
2. Description of Prior Art
An ion mobility spectrometer discriminates between different ions according to the fact that different ions have different velocities in a uniform weak electric field. The application of ion storage improves the sensitivity of the ion mobility spectrometer up to about an order of a pictogram. For the conventional ion storage as described in U.S. Pat. No. 5,200,614 and CN Patent 200310106393.6, for example, loss of ions occurs due to the poor boundary condition of the electrical field.
An ion storage trap used in a mass spectrograph is generally formed by end electrodes at both sides and a perforated intermediate electrode. The storage and extraction of ions are enabled by adjusting the voltages applied to the two end electrodes and the perforated intermediate electrode. Similarly to the ion storage trap used in the mass spectrograph, U.S. Pat. No. 6,124,592 provides a single ion storage method. In this method, however, the storage region has to be larger to meet the requirement of storage potential in the case of an ionization zone and a drift region each having a longer diameter. So, the ions have to travel a longer distance to exit from the storage region. This necessitates a longer gate-opening period and a higher volume. Further, inconsistency in the start points of different ions entering the drift region is increased.
U.S. Pat. No. 6,933,498 discloses an ion trap array-based storage solution to improve efficiency of ion storage. In this solution, between each of end electrodes and an intermediate electrode is sandwiched an insulator having holes, each of which corresponds to one ion storage trap. The ions may bump onto the insulator, causing charge transfer and accumulation and subsequent discharge. This will lead to instability in ion storage and degrade the sensitivity.